The pools, such as private or public swimming pools, are filled with a liquid such as water. The constant renewal of the water cannot be considered. However, the composition of the water is not stable and the quality of the water is likely to degrade. Now, it is necessary to ensure a certain usable comfort in order to comply with predetermined safety conditions. It is therefore routine practice to equip such pools with a water quality surveillance system. Such a system comprises sensors which can measure physico-chemical quantities representative of the quality of the water. The sensors are, for example, capable of measuring the temperature of the water, its pH, its conductivity, its oxidation-reduction potential (representative of the concentration of bactericide agent in the water, such as chlorine, bromine or active oxygen) in the water. The surveillance of the quality of the water makes it possible to trigger an appropriate treatment of the water. The current practice is to introduce suitable upkeep products, in appropriate quantities, in order to actuate a water oxygenation pump or else a water filtration device.
WO 2007/02530 discloses a floating surveillance system with a sensor installed capable of measuring a quantity representative of the quality of the water. However, the rate of false alarms with this type of device is high. The measurement of the quality of the water at a particular point of the pool is not necessarily representative of the quality of the water in the pool as a whole.
An immersion surveillance system is known which is installed on the side of the pool and includes a probe that is dipped into the water capable of detecting an acoustic wave generated by a body falling into the pool. However, the number of false alarms (detection of immersion without immersion event or absence of detection of immersion when an immersion event has occurred) is high. For example, taking into account the force of the wind, the damping of the swell provoked by a falling body can take some time, even not occur when the speed of the wind is greater than 36 km/h. This phenomenon degrades the sensitivity of the system.